An industrious 10 -year-old swimmer has attached an extension to his snorkel tube, so that he can sit on the bottom of the ocean for a longer period of time, watching the fish of the coral reef. What problems would you expect him to have? Assuming he is successful in breathing this way for a little while, what are some of the differences he will experience compared to normal breathing?
What will be an ideal response?
The resistance to air flow increases as a result of adding the extension to the snorkel tube. Assuming he has used an
extension of sufficiently large diameter, he is in a shallow location where the total length isn't excessive, and he has
the strength and endurance in his respiratory muscles, he may be able to breathe this way for a few seconds longer
than he could have held his breath. He will probably notice that he is breathing more deeply and at a higher rate, to
maintain ventilation against the higher resistance. After a few exchanges he will start to hypoventilate, despite his
efforts to increase pulmonary ventilation, because the presence of dead airspace in the tube will result in decreasing
PO2 in the alveoli. Dead airspace is a problem if the total volume of air in the tube is greater than the volume
exchanged with each breath.
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